In a large bowl, whisk together the flour, baking powder and salt. Set aside.

Melt the butter, and add the brown sugar, stirring until smooth. Allow the mixture to cool slightly. Add the eggs one at a time, beating well after each addition, then stir in the vanilla. Add the flour mixture, then the chocolate chips and nuts. Scoop the batter into the prepared pan.

Bake the bars for 30 to 35 minutes, until their top is shiny and golden. Don’t overbake, or the bars will be dry; a cake tester inserted in the center will not come out clean. Remove the bars from the oven, and allow them to cool to room temperature before cutting. Yield: 24 bars.